The present invention is directed to magnetic storage devices and in particular to a magnetic head loading assembly being pivoted to a carriage, said carriage being movable arranged in a radial direction with respect to a rotatable flexible magnetic medium.
Early magnetic storage devices for data processing systems made use of contact recording. This recording method was superceded to some extent after development of a bearing magnetic head with low mass expecially for mass storage devices, such as the magnetic disk storage device. With this improved type of head loading assembly the magnetic head is spaced away from the magnetic surface even during recording operations; i.e., the magnetic head is allowed to "fly" on a thin air layer over the recording medium so as to permit intimate interaction between the transducer and the magnetic surface. Contact recording has been used continuously, on the other hand, particularly with multi-channel devices, such as magnetic tape devices.
With rotatable magnetic storage media the head loading techniques were changed again when the so-called "floppy" disk systems were developed. In such storage systems, a thin flexible magnetic disk is used as storage medium in combination with low cost accessing, transducing and control apparatus. The low costs of this kind of storage devices have resulted in a widespread use for program storage, entry and control applications.
In the original floppy disk systems, the transducer structure generally comprises a single channel magnetic head having a contact surface. This contact surface is formed as a segment of a spheroid or at least in a curved shape. The transducer is mounted on a moveable carriage that is accessed to different circumferential tracks on the floppy disk. On the opposite side of the disk, and also in contact with the disk, is a pressure pad mounted adjacent to the end of a spring-loaded arm, which is solenoid-controllable so as to be free to exert pressure when data transfer operations are to take place.
Recently, however, floppy disk devices have been developed wherein both sides of the floppy disk are used for data transfer operations, the purpose primarily being to increase the storage capacity. Thus only a single low speed accessing mechanism continues to be employed. The magnetic heads are arranged on opposite sides of the flexible magnetic medium in a generally opposed relationship, with only a slight offset in the head gaps to avoid flux interaction.
As mentioned above, floppy disk storage devices are intended for a widespread use in a variety of applications due to their low cost. Therefore, it has been the main object with floppy disk storage devices, here more than with other storage devices, to achieve simple structures of high reliability for head loading carriage assemblies with sufficiently low access times and high storage capacity.
Present floppy disk manufacturers are using three approaches to double sided contact recording operations. One of these approaches is known from the U.S. Pat. No. 4,089,029 to Castrodale et al. With this type of magnetic recording device, in which a pair of transducers contact opposite faces of the recording medium, each of the transducers is mounted on a relatively weak gimbal spring. Relatively rigid load arms bear on dimples located at the centers of the transducers to form universal joint connections with the transducers. The load arms are mounted on relatively stiff gimbal spring portions for applying a predetermined force to the transducers. This known structure with the gimbal spring and universal joint connections allows the transducers to pitch and throw with wobbling movements of the recording medium. This is an effective solution in respect to accessing times and storage capacity. However, it is expensive and sensitive to adjustment.
Another magnetic recording device for double sided media is described in the U.S. Pat. No. 4,151,573 to Tandon et al. This device uses a fixed transducer on one side of the recording medium and a movable transducer element on the opposite side. The movable transducer is gimballed on a pivoted spring-loaded arm of low mass and high stiffness to urge the recording medium against the fixed transducer with a light force. The force is adequate, together with a slight penetration of the fixed transducer into the plane of the recording medium, to correct the deflections of the recording surface in a direction normal to the plane surface of the recording medium. It is suggested that the transducers are maintained in operative relation for maximum flux interchange, but without introducing undue wear or requiring a long head settling time. This known device has a simpler structure than the device mentioned above, but in both devices the magnetic transducers are in a loading position even if they are not operative, i.e. not in a recording or reproducing status.
Another known disk type magnetic recording system is described in the U.S. Pat. No. 3,814,441 to Craggs. This system employs apparatus for swinging the recording arm into position with the magnetic transducer centered within a given track and a stepping motor for stepping the transducer from track to track. The system also includes a safety lifting device which is provided for preventing excessive wear of any one track. The safety lifting device is under the control of a solenoid which, in turn, is energized through a timer. This timer is set when any of several operating controls are activated and reset after a predetermined period of time. By resetting the timer the solenoid is de-energized and the recording arm is released automatically. This is accomplished by a load spring which works against the solenoid so that there is always a positive arm lifting movement providing a fail-safe operation. By this fail-safe operation undue wear is totally avoided, but, on the other hand, this system requires long head settling times.